VrShell: Allow native control of UI element opacity.

chrome/browser/android/vr_shell/ui_scene.cc

Index: chrome/browser/android/vr_shell/ui_scene.cc
diff --git a/chrome/browser/android/vr_shell/ui_scene.cc b/chrome/browser/android/vr_shell/ui_scene.cc
index 2d4adb13181229d86665b66925900a5b649193b6..3186ee634a23c4ed78232f99c5d1cba23cf448af 100644
--- a/chrome/browser/android/vr_shell/ui_scene.cc
+++ b/chrome/browser/android/vr_shell/ui_scene.cc
@@ -96,6 +96,9 @@ void ParseEndpointToFloats(Animation::Property property,
     case Animation::Property::TRANSLATION:
       ParseFloats(dict, {"x", "y", "z"}, vec);
       break;
+    case Animation::Property::OPACITY:
+      ParseFloats(dict, {"x"}, vec);
+      break;
   }
 }
 
@@ -324,7 +327,9 @@ void UiScene::UpdateTransforms(float screen_tilt, int64_t time_in_micro) {
   for (auto& element : ui_elements_) {
     element->transform.MakeIdentity();
     element->transform.Scale(element->size.x, element->size.y, element->size.z);
-    ApplyRecursiveTransforms(*element.get(), &element->transform);
+    element->computed_opacity = 1.0f;
+    ApplyRecursiveTransforms(*element.get(), &element->transform,
+                             &element->computed_opacity);
     element->transform.Rotate(1.0f, 0.0f, 0.0f, screen_tilt);
   }
 }
@@ -352,19 +357,21 @@ UiScene::UiScene() = default;
 UiScene::~UiScene() = default;
 
 void UiScene::ApplyRecursiveTransforms(const ContentRectangle& element,

[mthiesse, 2017/01/11 18:33:04]

Unrelated, but can you add a TODO to be smarter about how we compute these
transforms? We could theoretically be doing a single pass.

[cjgrant, 2017/01/11 18:53:07]

Agreed.  There are multiple bits to this though:
1. Don't recompute parent transforms multiple times in the render loop.
2. Don't recompute transforms (other than pose-related) for elements that
haven't changed (animation or explicit update).

In lieu of shuffling the whole implementation to a tree structure, we could put
a dirty bit on the computed transform, and keep the recursive approach.  Dirty
bits would be cleared once per render cycle.  That addresses (1).  To achieve
(2), I think we need element changes to clear dirty bits of child elements as
well, and currently parents aren't aware of their kids (sounds blissful).

Thoughts?

[mthiesse, 2017/01/11 19:02:49]

Speaking as someone who's never had children, a dirty bit sounds like a good
idea.

[cjgrant, 2017/01/11 20:58:42]

Done.  Filed crbug/680253.

-                                       ReversibleTransform* transform) {
+                                       ReversibleTransform* transform,
+                                       float *opacity) {

[mthiesse, 2017/01/11 18:33:04]

float*

[cjgrant, 2017/01/11 20:58:42]

Done.

   transform->Scale(element.scale.x, element.scale.y, element.scale.z);
   transform->Rotate(element.rotation.x, element.rotation.y,
                     element.rotation.z, element.rotation.angle);
   transform->Translate(element.translation.x, element.translation.y,
                        element.translation.z);
+  *opacity *= element.opacity;
 
   if (element.parent_id >= 0) {
     const ContentRectangle* parent = GetUiElementById(element.parent_id);
     CHECK(parent != nullptr);
     ApplyAnchoring(*parent, element.x_anchoring, element.y_anchoring,
                    transform);
-    ApplyRecursiveTransforms(*parent, transform);
+    ApplyRecursiveTransforms(*parent, transform, opacity);
   }
 }
 
@@ -385,6 +392,10 @@ void UiScene::ApplyDictToElement(const base::DictionaryValue& dict,
   ParseVec3f(dict, "scale", &element->scale);
   ParseRotationAxisAngle(dict, "rotation", &element->rotation);
   ParseVec3f(dict, "translation", &element->translation);
+  double opacity;
+  if (dict.GetDouble("opacity", &opacity)) {
+    element->opacity = opacity;
+  }
 
   if (dict.GetBoolean("contentQuad", &element->content_quad)) {
     if (element->content_quad) {